The major inducible heat shock protein (72 kDa HSP) increases canine distemper virus and measles virus (MV) nucleocapsid transcriptional activity, resulting in increased in vitro cytopathic effect. The first specific aim of this proposal will test the hypothesis that a 7 amino acid HSP binding motif on the exposed carboxyl terminus of the nucleocapsid (N) protein of MV mediates the functional interaction between kDa HSP and nucleocapsid (NC). The binding reaction between 72 kDa HSP and NC will be characterized for ribonucleoprotein complexes containing either intact N or N in which the carboxyl terminus has been removed by limited proteolysis. Synthetic peptides mimicking the motif will then be tested for their ability to (a) inhibit NC binding by HSP and (b) inhibit HSP-mediated stimulation of NC transcriptional activity. Finally, variations of this amino acid sequence mediating either high or low affinity HSP interaction will be incorporated into recombinant Edmondston-MV (Ed-MV) to directly test the role of this motif in mediating viral stress responsiveness and in vitro cytopathic effect. The second specific aim of this proposal will test the hypothesis that elevated expression of 72 kDa HSP in brain enhances neurovirulence of HV strains containing high-affinity HSP binding motifs whereas neurovirulence of strains containing low-affinity HSP binding motifs will be unaffected. This specific aim will use available transgenic C57 mice that over-express 72 kDa HSP in neurons and recombinant infectious virus generated in specific aim one. Preliminary data show that intracranial inoculation of neonatal mice with Ed-MV causes a chronic persistent infection of brain in 65% of inoculated animals, such that enhanced viral gene expression mediated by elevated 72 kDa HSP should be manifest as increased lesion severity and/or the emergence of acute disease. Results of these studies can thus establish both viral and cellular determinants of neurovirulence and may lead to the development of novel approaches for treatment of viral encephalitis based upon inhibition of virus-HSP interaction.